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arXiv · 0705.0668

Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2

E. Wawrzynska·R. Coldea·E. M. Wheeler·I. I. Mazin·M. D. Johannes·T. Sorgel·M. Jansen·R. M. Ibberson·P. G. Radaelli
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Abstract

We report a high-resolution neutron diffraction study on the orbitally-degenerate spin-1/2 hexagonal antiferromagnet AgNiO2. A structural transition to a tripled unit cell with expanded and contracted NiO6 octahedra indicates root(3) x root(3) charge order on the Ni triangular lattice. This suggests charge order as a possible mechanism of lifting the orbital degeneracy in the presence of charge fluctuations, as an alternative to Jahn-Teller distortions. A novel magnetic ground state is observed at base temperatures with the electron-rich S = 1 Ni sites arranged in alternating ferromagnetic rows on a triangular lattice, surrounded by a honeycomb network of non-magnetic and metallic Ni ions. We also report first-principles band-structure calculations that explain microscopically the origin of these phenomena.

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E. Wawrzynska, R. Coldea, E. M. Wheeler, I. I. Mazin, M. D. Johannes, T. Sorgel, M. Jansen, R. M. Ibberson, P. G. Radaelli. 2007-08-29. Orbital degeneracy removed by charge order in triangular antiferromagnet AgNiO2. https://doi.org/10.1103/physrevlett.99.157204

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